1. Field of the Invention
The present invention relates to an aircraft window of synthetic resin having a hard coated film, such as a cabin window, a cockpit window (mainly a side panel), a canopy or windshield, and a method for producing the same.
2. Description of the Related Art
Synthetic resin such as polycarbonate or polyacrylate resin has been in common usage as aircraft windowpanes in light of the balance of performances such as transparency, strength, specific gravity and durability. Polyacrylate resin has good moldability and easily obtainable optical isotropy in case of producing a large size molding body. Polycarbonate has excellent heat resistance and impact load carrying capacity. These resins have been applied to the windowpane of many kinds of aircrafts, taking advantage of each property above.
Meanwhile, aircraft windowpanes have a lot of occasions to be subject to abrasive damage caused by abrasion with atmospheric ice particles or raindrops, by contact with inorganic particles such as volcanic ash or clouds of sand or by contact with insects sticking to the surface of the windowpanes. The surface is wiped with cleaning cloth or the like when in maintenance and cleaning. Though these resins have no problem with bulk strength, the surface hardness thereof is low so that the surface is apt to become scratched. This is the only difficulty because the aircraft window should have good visibility. A frequent exchange of windowpanes brings about increasing maintenance costs, which is no measure for solving the problem. Hence, recently, an aircraft window mounted with a resin windowpane having a surface protective coating has been desired.
However, conventional methods for applying a protective coating can be roughly categorized by (1) a method for forming a SiO2 film by coating a compound having Si and baking it or by (2) a method for forming a SiO2 film by PVD such as ion-plating. The method (1) gives insufficient hardness of the surface so that the protection goal cannot be attained. The method (2) generates peeling or cracks of the film due to poor adhesion and does not give sufficient protection because of difficulty in obtaining a thick film.
In view of the need to solve the prior problems, it is the object of the present invention to provide an aircraft window of synthetic resin having a hard coating with excellent hardness and durability in an aircraft cabin window having at least a double-pane construction with a hollow interspace therebetween or an aircraft cockpit, canopy, or windshield window having a single pane construction including a monolayer or multilayer pane and to provide a method for producing the same.
An aircraft window of synthetic resin having hard coated film and at least a double-pane construction with a hollow interspace therebetween for an aircraft cabin window according to the present invention comprises an outer synthetic resin molded body having hard coated film on the outside surface of the aircraft and an inner synthetic resin molded body. The bodies face each other to form at least a double-pane construction with a hollow interspace therebetween. The hard coated film comprises siloxane bonds and/or silazane bonds obtained by coating a coating composition containing perhydropolysilazane or its condensation polymer which is substantially soluble in organic solvent on the surface of the synthetic resin molded body and heat-treating the body at approximately ambient temperature to 100xc2x0 C. in air or humidified air.
An aircraft cabin window should have a heat-insulating property because of the extreme temperature difference between the inside and the outside of the cabin, transparency, and strength as a member constructing a part of the fuselage and to endure the pressure difference between the inside and the outside of the cabin. Furthermore, a fail-safe structure includes measures in case the pane is damaged. Therefore, the aircraft cabin window has at least a double-pane construction with a hollow interspace between facing transparent synthetic resin molded bodies.
According to the present invention, one side (the outside of the cabin) of at least one of the molded bodies has the hard coated film. At least double-pane construction means that, if needed, a multi-pane construction, beyond double-pane construction, is adopted. This improves the insulating function and the failsafe function. In this case, the hard coat is indispensably needed on the molded body inside of the cabin where abrasion rarely occurs.
Thus, for example, one side of a transparent molded body of synthetic resin such as polycarbonate or cast acrylate resin is coated with a solution of substantially organic-solvent-soluble perhydropolysilazane or its condensation polymer in an organic solvent so that the film thickness after heat-treating codes to be from 1 xcexcm to 100 xcexcm and the coated body is heat-treated at approximately ambient temperature to 100xc2x0 C. after drying in air. A hard film having silazane bonds and/or siloxane bonds is coated on the one side of thus obtained transparent molded body of synthetic resin such as polycarbonate or cast acrylate resin. A window part comprises the two bodies bonded together with a spacer inserted at the outer perimeter therebetween. The faces having no hard coating of the two bodies are facing each other so as to be spaced apart from one another. The window part is fixed to an opening of the fuselage for a window through a gasket or a sealing member to form a cabin window. In this case, a gasket or a sealing member may be molded so that the two bodies are spaced apart from one another when the two bodies are fixed through the gasket or the sealing member and a two-pane construction is formed by fixing one, body by one body to the gasket or the sealing member.
The cast acrylate resin is a transparent synthetic resin having a high softening point consisting of a homopolymer or a copolymer obtained by polymerizing a polymerizable monomer consisting mainly of methyl methacrylate. The synthetic resin is cast to a panel-formed molded body by heating to flow to a temperature equal to or higher than the softening point thereof. A windowpane can be made from the panel-formed molded body by cutting to a form of the windowpane. A windowpane can also be made by casting the resin to a form of the windowpane. A method other than these is to pour the monomer into a board-formed mold to cast and polymerize at the same time.
The thickness of the transparent molded body of synthetic resin is variable according to the intended strength of the fuselage or the size of the opening of the fuselage. The spacer may be made from the same material as the transparent molded body of synthetic resin or from more elastic material than that of the body. The gasket or the sealing member is selected from organic materials having appropriate elasticity, strength and durability in order to keep the cabin airtight from the outside, where the temperature difference is great, and to firmly support the windowpanes.
One of the perhydropolysilazane or its condensation polymer which is substantially soluble in organic solvent in the coating composition is a cyclic or linear perhydropolysilazane having a structure of the formula (1) as a repeated unit or a mixture thereof. 
Further, another of the perhydropolysilazane or its condensation polymer is an intermolecular dehydrogenation condensation polymer of cyclic or linear perhydropolysilazanes having a structure of the formula (1) as a repeated unit or a mixture of them.
Furthermore, another of the perhydropolysilazane or its condensation polymer is a dehydrogenation condensation polymer having a plurality of the condensation structures of (2) or (3) by condensing the cyclic or linear perhydropolysilazane having a structure of (1) with ammonia or hydrazine or condensing the mixture of the cyclic and linear perhydropolysilazane having a structure of (1) with ammonia or hydrazine. 
A hard coated film having siloxane bonds and/or silazane bonds according to the present invention has the bonds formed by coating the silazane compound and heat-treating, the silazane bond being indicated by the formula (4) and the siloxane bond being indicated by the formula (5).
xe2x80x94Sixe2x80x94Nxe2x80x94xe2x80x83xe2x80x83(4)
xe2x80x94Sixe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(5)
According to the present invention, an aircraft window of synthetic resin having hard coated film and a single pane construction including a mono-layer or multi-layer pane for an aircraft cockpit, canopy, or windshield window comprises a synthetic resin molded body having hard coated film on the outside surface or both outside and inside of the aircraft to form a single pane construction of mono-layer or multi-layer. The hard coated film comprises siloxane bonds and/or silazane bonds obtained by coating a coating composition containing perhydropolysilazane or its condensation polymer which is substantially soluble in organic solvent on the surface of the synthetic resin molded body and heat-treating the body at approximately ambient temperature to 100xc2x0 C. in air or humidified air.
An aircraft cockpit, canopy, or windshield window is exposed to more severe conditions than a cabin window is exposed to. Collision chances with foreign matter are more frequent and the impact is higher. The windowpane is not only a plane surface but also a curved surface. There is another requirement of clear visibility so that irregular refraction of penetrated light is not allowed. Thus, the windowpane cannot be a double-pane construction as a cabin window.
Accordingly, a multi-layer laminated structure is necessary in order to attain sufficient failsafe function for single pane construction even if it has a curved surface. High strength resin such as stretched polyacrylate resin is used for a main structural part. Stretching strengthens the resin because the molecular arrangement turns regular thereby. The tensile strength, compression strength and other strength of the resin are far higher than those of cast polyacrylate resin, and moldability and transparency remain. Material sandwiched between the stretched polyacrylate resins is selected from high adherence resins which absorb the thermal expansion or shrinkage stress by the temperature difference between outside and inside of the fuselage and do not affect the other layer when the one layer gets cracked, though the material is not restricted. An electrically conductive film heated by electric current may be sandwiched in order to prevent bedewing, icing or hazing in addition to the aforementioned structural function.
The windowpane having a multi-layer laminated structure has a hard coated film on the inside surface of the fuselage or hard coated films on the both inside and outside surfaces, because the inside surface is also apt to get scratched, which is different from the cabin window. A single-layer windowpane also has both cases stated above for the same reason.
According to the present invention, a synthetic resin molded body of the aircraft window of synthetic resin having hard coated film comprises a polyacrylate resin molded body or a polycarbonate resin molded body. The polyacrylate resin preferably comprises a cast polyacrylate resin or a stretched polyacrylate resin.
Various kinds of heretofore known perhydropolysilazanes or their condensation polymers can be used as perhydropolysilazane or its condensation polymer, which is substantially soluble in organic solvent, according to the present invention. For example one of the above compounds is a cyclic or linear perhydropolysilazane having a structure of the formula (1) as a repeated unit or a mixture thereof, which can be produced by a method disclosed in Japanese laid open publication P1984-207812A.
Another example of perhydropolysilazane or its condensation polymer, which is substantially soluble in organic solvent is a compound obtained by heating to dehydrocondense a cyclic or linear perhydropolysilazane having a structure of the formula (1) or a mixture thereof in an alkaline solvent or in a solvent containing an alkaline compound. An example of the methods for producing the compound is disclosed in Japanese laid open publication P1989-138108A.
Another example of perhydropolysilazane or its condensation polymer, which is substantially soluble in organic solvent, is a compound obtained by heating to dehydrocondense a cyclic or linear perhydropolysilazane having a structure of the formula (1) or a mixture thereof through ammonia or hydrazine. An example of the methods for producing the compound is disclosed in Japanese laid open publication P1989-138107A.
The molecular weight of perhydropolysilazane or its condensation polymer is not particularly restricted but preferably as high as it gives a good film and not as high as it gives appropriate workability by being substantially soluble in an organic solvent for coating and having enough liquidity.
The hydrogen elements are preferably not consumed completely, but remain partially unreacted, which is related to the adherence of the hardened film, whereby a strongly adhered hardened film can be formed on the synthetic resin surface.
A solvent for coating perhydropolysilazane or its condensation polymer on the surface of the sythetic resin is preferably a solvent which is not reactive with SiH group. Compounds which have active hydrogen atoms such as alcohol, primary amine, secondary amine or water containing solvent should be avoided. Thus an appropriate solvent is, for example, aliphatic, alicyclic or aromatic hydrocarbon, halogenated hydrocarbon, and aliphatic or alicyclic ether. Further, a mixture of more than two kinds of solvents can be used for adjusting the solubility of the synthetic resin to the solvent or the evaporation rate of the solvent. But a solvent that dissolves the synthetic resin well is inappropriate. Some kinds of aromatic hydrocarbon, ketone or ester fall into this category. Therefore, an appropriate compound should be selected as a solvent, or a non-solvent of these resins is mixed to adjust the solubility.
A coating composition containing a substantially organic solvent soluble perhydropolysilazane or its condensation polymer used in the present invention is a known composition which is made and sold by Clariant Japan K.K. It is sold as a product name of polysilazane silica coating L110, L710, N110, V110, D110 and L120. These are 20% xylene or dibutylether solution of perhydropolysilazane having an average number average molecular weight of 700-1000 with or without an added oxidation condensation catalyst. Each product is named according to the kind of solvent, molecular weight, and the kind of catalyst including with or without catalyst.
Coating on the surface of the molded resin body is performed by known methods such as dipping, spraying, brush coating, spin coating, roll coating or doctor-blade coating. After coating, solvent is evaporated at low temperature and the coated resin body is heat-treated at prescribed temperature. The heat-treating environment can be chosen from among humidified air, dry air, humidified inert gas and dry inert gas. The higher the partial pressure of water or oxygen is, the more rapidly the film is formed at low temperature, since the rate of reaction at low temperature becomes more rapid. Further, if a coating composition containing an oxidation condensation catalyst is used, it is possible to form more rapidly a coating film at lower temperature.
Further, according to the present invention, an aircraft window of synthetic resin having hard coated film comprises a monolayer hard coated film whose thickness is 1 xcexcm or more and less than 10 xcexcm after coating the coating composition on the surface of the molded resin body and heat-treating in air or humidified air.
In a conventional hard coating, a protective coating is formed by coating a coating composition containing a compound of silicon to which alkoxy groups are bonded, generating siloxane bonds through the steps of hydrolysis and dealcoholization or dehydration. Unlike with a film forming mechanism of the present invention, as bulky, high molecular alkoxy groups are broken away, causing decrease of molecular weight of the polymer resulting from the film forming reaction, the film has low density and poor adherence. Alkoxy groups often remain depending on a reaction condition, giving a film of low density and poor adherence. Therefore, a film thickness formed by this kind of reaction has its limits of 1 xcexcm at most. A film of more than 1 xcexcm results in generation of cracks or deterioration of adherence by heat cycle to become far from practical use. Such :thin film coated on an aircraft window has poor durability so that a condition of cleaning work becomes severe because the work of taking off the dirt on the outside of the fuselage needs to be frequent.
When a hard coated film having siloxane bonds and/or silazane bonds is formed by coating a coating composition containing perhydropolysilazane or its condensation polymer which is substantially soluble in organic solvent on the surface of the molded synthetic resin body and heat-treating the body at approximately ambient temperature to 100xc2x0 C. in air or humidified air according to the present invention, the film forming mechanism contains conversion to siloxane bonding through hydrolysis, oxidation, deammonization and dehydration. The molecular weight of the resultant film polymer is essentially larger than that of perhydropolysilazane and there is no large organic group eliminating from perhydropolysilazane so as to give a very dense and adherent film. Therefore, the film thickness of 1 xcexcm or more enables one to obtain the hardness to attain the object of the present invention. The object is to obtain a coated film having high durability, enough hardness to bear abrasion, and good adherence, including improvement of conditions in cleaning an aircraft window.
However, durability in the thermal cycle test begins to lower with the mono-layer film when the film thickness comes to 10 xcexcm or more, causing cracks and peeling off of the film to happen.
According to the present invention, a hard coated film of an aircraft window of synthetic resin comprises substantially two layers of an intermediate layer which coats the top surface of molded resin body and an outermost layer which coats the top surface of the intermediate layer. After the molded resin body is coated with the coating composition and heat-treated in air or in humidified air, a coated film thickness of two layers in total is 10 xcexcm or more and 200xcexcm or less.
Thus, a very thick-coated film can be formed when the resin surface is coated with two layers according to the present invention. The coated film of an aircraft window is exposed to very severe conditions, as is well known, and should endure a broad range of temperature conditions of 80xc2x0 C. under direct rays of the sun in a tropical zone or under friction heat of high speed flying to xe2x88x9250xc2x0 C. under high-altitude or high-latitude flying. If an aircraft flies at supersonic speed, the coated film of the aircraft window should endure a broader temperature range of xe2x88x9270 to 120xc2x0 C. If the harder film is coated to ensure abrasion resistance, thermal or other stress of expansion-shrinkage cycles due to a difference of thermal expansion between the film and substrates such as polyacrylate resin or polycarbonate resin causes cracks. Thus if the film thickness is secured by one layer, a thickness of 10 xcexcm is the limit because of the above reason.
Hence, the present inventors tried a surface treatment comprising steps of coating perhydropolysilazane free from catalyst, a composition of the kind which does not harden at low temperature such as N510 or N310 and of heat-treating at 80-100xc2x0 C. When coating perhydropolysilazane free from catalyst, silazane is not perfectly converted to siloxane, but partially remains by the heat-treatment such extent so as to form a soft and flexible coated film of an intermediate layer. When perhydropolysilazane containing catalyst is coated on the top of an undercoating layer (intermediate layer) and heated to prescribed hardness, and even the thickness of the coated film comes to 200 xcexcm ih total, the intermediate layer absorbs stress in the undercoating layer so that cracks or peeling-off do not occur, even after the heat cycle. Such double layer coating enables a hard protective coated film of sufficient thickness.
Since silazane bonding remains in the undercoating layer, it is apprehended that a property of the film may change with time by reacting with water in the air. It would appear that the outermost layer coating functions as a barrier coating so as to block off water or oxygen. Consequently, the double layer coating has good durability.
A practical application of the hard coated film is impossible without double coating, including the undercoating layer according to the present invention, in the case of a canopy or a windshield for which a thick hard coating is necessary. Double coating is not indispensable for a coating for a cabin window of a passenger carrier as thin film thickness can be applicable.
According to the present invention, a hard coated film thickness of the intermediate layer in an aircraft window of synthetic resin having hard coated film is between 1 xcexcm and 50 xcexcm. The undercoating layer having a thickness of less than 1 xcexcm is not effective as an intermediate layer; the undercoating layer having a thickness of more than 50 xcexcm negatively affects the strength of the coated film in total because the intermediate layer is comparatively soft.
According to the present invention, in an aircraft window of synthetic resin having a hard coated film, the coating composition for a monolayer coated film or the coating composition for the outermost layer of a double-layer coated film contains paradium catalyst. A large oven for high temperatures is necessary in order to heat-treat a large molded body such as an aircraft window of synthetic resin. Thus, it is advantageous to react at low temperature at high reaction rate by an effective catalyst such as paradium. The coated film may also be hardened in an atmosphere of a vapor of an alkaline compound having no reactive hydrogen such as trialkylamine as a catalytic measure for accelerating the reaction.